Pipes for a recuperator



Feb. 21, 1967 H. JACOBS PIPES FOR A RECUPERATOR 3 Sheets-Sheet l Filed April 13, 1965 INVENTOR. /VBIZp aCQS Feb. 21, 1967 H. JACOBS PIPES FOR A RECUPERATOR Filed Abril 13, 1965 3 Sheets-Sheet 2 INVENTOR.

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Feb. 21, 1967 Filed Abril 13, 1965 INVENTOR. Hezz Jacos BY v mu, whfl m w# United States Patent O 5 Claims. 165-145 This invention relates to a recuperator equipped with pipes through which flows air to be warmed. Preferably these pipes are made of cast-iron and have an oval or similarly shaped cross-section. Generally, the pipes are in a channel through which traverses heated flue gases (products of combustion of a fuel) and are arranged substantially transversely of the heated gas flow 'and so that the longer cross-sectional axis of the pipes lies in the direction of flow of the flue gases. The pipes are disposed in multiples side `by side and next to one another and behind one another. The surface areas of the pipes are enlarged, for example, by ribs on their inner and/or outer walls.

While the invention is especially applicable to cast-iron pipes, it is not limited thereto. Cast-iron pipes aiford 'an opportunity of having their surface, to a great extent, made in optional configurations on both sides of the heat transfer area, in other words, the surface of the inner wall as well as of the outer wall of the pipe may have an optional or random shape. Thus, when space is limited, it is possible to obtain favorable heat transfer values. Moreover, in addition to having stronger walls and greater durability, cast-iron pipes also have high res-istance to corrosion and scaling. Ho'wever, one disadvantage to cast-iron pipes is formation of thermal stresses caused by rigidity of the pipes.

Cast pipes with ribbed inner walls require a large crosssection, and this calls for a relatively large extended area of the pipe cross-section in the direction of flow of the fuel gas or flue gas. Thus a pipe cross-section of oval, oblong or similar configuration is required, and the longer cross-sectional axis must extend substantially in the direction of flow of the flue gas. Such configuration results in a considerable difference in temperature between that face of the pipe on which the flue gases first impinge and the remaining cross-sectional area of the pipe. To some extent, this can generate considerable thermal stress in the cast material when the pipes are of rather great length. The same occurs in similar degree to rolled or fabricated pipes.

In recuperators which operate exclusively convectively, the difference in temperature between the pipe face on which the flue gases impinge and the remaining crosssectional portions is tolerable. In a bundle or group of pipes formed by pipes disposed adjacent to and behind one another, when the entry temperature of the flue gas is high, the front side of those pipes which'are first in line in the direction of flow is especially subjected to additional thermal radiation. Accordingly, t here are particularly strong thermal stresses here, and these pipe portions p are exposed to especially high temperatures.

This invention provides a recuperator, in particular one with cast-iron pipes, which avoids the temperature diflerences encountered in the pipes and the thermal stresses generated thereby, so that the recuperator may be operated with a flue gas temperature which is as high as possible.

To this end, in =a recuperator of the above-named type and in accordance with the invention, the surface area of the outer wall in the forward portion of one embodiment and in the forward third of a second embodiment of the Patented Feb. 21, 1967 pipe cross-section relative to the direction of flow of the flue gases, is smaller, and the surface area of the inner wall in this forward portion is larger than the remaining cross-sectional portion -or portions. This results -in a small heat transfer area or surface on the flue gas side of the outer surface of the pipe facing the flue gas flow, while at the same time the inner wall of the same crosssectional portion has an enlarged surface area.

P-referably, the outer wall has no ribs on the forward third of the pipe cross-section. The outer wall of a middle cross-sectional third has expanding ribs which attain their full size in a final third of the pipe crosssection, in other words, in that third which is farthest removed from first impingement of the flue gas upon the forward third of the pipe cross-section. The ribs of the inner wall are preferably larger or have greater surface area in the middle cross-sectional third of the pipes than those ribs which are located behind them with respect to the direction of flow of the flue gases. In the rear cross-sectional third of the pipe, the interior is free of ribs, with the result that in the direction of flow of the flue gases there is a gradual increase in surface area on the outer wall of the pipe, and a corresponding decrease in surface area on the inner wall of the pipe. The foregoing is applicable to that embodiment of the invention which has two portions of cross-section; namely, a forward portion and a rear portion.

The interior of the pipes may be provided with a displaoement body or member which is shaped to conform to the configuration of the interior space of the pipes.

Depending upon requirements, some recuperators equip only those pipes, which are first in line in the direction of flow of the fuel gases, with the above described ribs to increase the surface areas of certain parts of the inner and outer walls thereof. v

In the accompanying drawings I have shown a preferred embodiment of a recuperator in accordauce with my invention in which: a

FIG. 1 is a fragmentary side elevation View partially insection shown air pipes installed in a flue gas channel and arrangedin two groups or bundles.

FIG. 2 is a plan View of the recuperator of FIG. 1.

FIG. 3 is a section view through one of the pipes and along the line III--III of FIG. 1.

FIG. 4 is 'a section view along the line IV-IV of FIG. 3.

FIG. 5 is a view of a portion of the outer pipe wall along the line V-V of FIG. 3.

3 FIG. 6 is a section View -along the line VI--VI of FIG.

FIG. 7 is a view similar to FIG. 3 and showing a displacement member in an air pipe.

The recuperator of FIGURES l-7 comprises .an upper air distribution chamber 1 into which the air to be heated enters and is distributed to pipes R 'below the chamber 1 and which form a pipe bundle or group I. The pipes R connect into a lower collector chamber 2 from which a transfer Conduit 3 leads to a lower distribution chamber 4. Pipes R of a pipe bundle II extend vertically from this lower distribution chamber 4 to an upper collector chamber 5 from w hich the heated air is withdrawn. Pipes R and R of pipe groups I and II are disposed vertically in a flue gas channel 6, so that the direction of flow of the flue gases which is indicated by arrow 7 is at right angles to pipes R and R and thereby also at right angles to the direction to flow of the air to be :heated in the pipes.

The pipes have an oblong cross-section and are rounded on their narrow sides, so that in cross-section they resemble an oval. They are so arranged in the channel 6 and with respect to chambers 1, 2, 4 and 5 that their longer cross-sectional -aXis lies in the direction of flow of the flue gases.

Due to direct impngement of the hot flue gases and to the reflection of heat from the flue gas channel walls, the front faces 8 particularly of the first pipes R of pipe bundle II are additionally heated intensely by radiation. Side 9 of the pipes is turned away with respect to the direction of flow of the flue gasses and accordingly is heated less intensely as are the flanks 10 of these pipes. This difference in the heating of the cross-sectional portions of the pipes generates therrnal stresses.

In order to avoid or overcome the thermal stresses, outer wall A of the pipes, and particularly of pipes R has been left without ribs on that third of the pipe cross- *section which faces the flue gas entry, in other words, the

outer wal portion of front face 8 is made without ribs up to line L which defines a forward third from a middle third. Therefore, this front third has a lesser amount of surface area on the outer wall than the back or rear third of the pipe cross-section considered in respect to the direction of flow of the flue gases (ef. arrow 7 in FIGS. 1 to 3). This rear third has ribs 11 on its outer wall. These ribs extend full size from line L; which defines the middle or central third from the rear third of the pipe cross-section to the back end of the pipe cross-section. Between lines Lz and L of the central third, the ribs decrease in size such as at 12 and accordingly have a smaller amount of surface area than those portions of the ribs 11 along the rear third of the pipes.

The ribs 1 are disposed parallel to the direction of flow of the flue gases, thus offering no signiflcant resistance to the flow of said gases.

Inner wall J of the pipe cross-section has its front third provided with ribs 13 whose size is the same over the full length of this front third of the cross-section. In the middle third, however, between lines L and L the height of the ribs 14 decreases, th-us making the amount of surface area of the inner wall in this thir-d smaller than the amount of surface area between front face 8 and limit line L In the back third, between line L and side 9, the inner wall has only small ribs or none at all. As shown, the ribs 13 extend in the direction of flow of the air through the pipes R and R The increase in amount of surface area of the outer wall A of the pipe cross-section, when considered in the direction of flow of the flue gases, corresponds approximately to the decrease in amount of surface area of the inner wall of the pipe cross-section also considered in the direction of flow of the flue gases. As shown in FIG. 3, the outer ends of the ribs 14 of one wall Side run approximately par-allel to the slopng edge F of ribs 11 which may be interrupted as at 20.

The interior of pipes R and R may contain a displacement body 15 (FIG. 7) provided with an enlarged portion 16 which conforms to the pear-shaped configuration of interior space 17 of the rear third of the pipes. otherwise the -construction of the pipes is the same as that of FIGS. 2 to 5 in which the 'cast-iron pipes are provided at their ends in conventional manner with cast-on steel collars 18 which have a compensatory throat 19.

Although the FIGURES 1-7 relate to a three portion pipe cross-sectionwise in the direction of flow of the fuel gases, the foregoing features can be utilized in pipe whose cross-section comprises two portions instead of the three portion,

While I have shown and described a preferred embodiment of my invention, it may be otherwise embodied within the soope of the appended claims.

I claim:

1. In a recuperator having a channel through which heated gases flow and at least one pipe through which air to be heated flows parallel to the axis of the pipe, said pipe being positioned in the channel transversely of the flow of heated gases, the improvement in the pipe which comprises,

(A) external ribs on the outside of said pipe extending parallel to the direction of flow of the hot gases and spaced from each other along the longitudinal length of the pipe and inreasng in area exposed to hot gases aft of the forward portion of said pipe (in the direction of gas flow) to the rearward portion of the pipe, and

(B) internal ribs on the inside of said pipe extending parallel to the axis of said pipe, inwardly towards the axis of said pipe, and spaced from each other across the inside surface of the pipe, successive ribs (in the direction of hot gas flow) decreasing in area exposed to the flow of air to be heated from the forward portion of said pipe to su bstantially the rearward portion of said pipe.

2. The improvement in a recuperator pipe as described in claim l in which the external ribs extend from the first portion of the external surface of the pipe which is free from impingement of hot gases.

3. The improvement ina recuperator pipe as described in claim 1 in which the internal ribs extend along only that portion of the pipe which is exposed to impingement of hot gases.

4. The improvement in a recuperator pipe as described in claim 1 in which the pipe is oblong in cross-section with a first section having a curved wall exposed to impingement of hot gases, a middle section, and a third section having a curved wall opposite said first wall and removed downwardly in the direction of the flow of hot gases from the first curved wall, and in which the external ribs eXtend from a point between the first and middle sections and increase in area as they extend rearwardly along said middle section and continue the maximum area which they obtain in the middle section along the third section and in which the inner ribs have their maximum area in the first section and decrease in area in the middle section.

5. The improvement in a recuperator pipe as described in claim 1 in which a displaoement member is positioned centrally ir said pipe and extends parallel to the flow of hot gases.

References Cited by the Examiner UNITED STATES PATENTS 2,029,450 2/1936 Truelson l65--180 X F OREIGN PATENTS 769,888 6/1934 France. l,280,992 11/ 1961 France.

445,152 2/ 1926 Germany. 411,3l9 7/1934 Great Britain.

ROBERT A. OEARY, Prmary Exami er, I. W. STREULE Assistant Eaw'ner, 

1. IN A RECUPERATOR HAVING A CHANNEL THROUGH WHICH HEATED GASES FLOW AND AT LEAST ONE PIPE THROUGH WHICH AIR TO BE HEATED FLOWS PARALLEL TO THE AXIS OF THE PIPE, SAID PIPE BEING POSITIONED IN THE CHANNEL TRANSVERSELY OF THE FLOW OF HEATED GASES, THE IMPROVEMENT IN THE PIPE WHICH COMPRISES, (A) EXTERNAL RIBS ON THE OUTSIDE OF SAID PIPE EXTENDING PARALLEL TO THE DIRECTION OF FLOW OF THE HOT GASES AND SPACED FROM EACH OTHER ALONG THE LONGITUDINAL LENGTH OF THE PIPE AND INREASING IN AREA EXPOSED TO HOT GASES AFT OF THE FORWARD PORTION OF SAID PIPE (IN THE DIRECTION OF GAS FLOW) TO THE REARWARD PORTION OF THE PIPE, AND 